Vehicle drive lines transmit torque or power from a drive source, such as an internal combustion engine, to vehicle wheels. The torque or power may be transmitted through a series of driveline components such as gears, joints, and shafts. The driveline components provide a level of torsional stiffness to satisfy performance requirements. The driveline components also provide a level of compliance to reduce unwanted noise, vibration, or harshness. Some vehicle drive lines include drive shafts that are a simple one-piece torque transmitting shaft having a single torsional stiffness rate.
Accordingly, it is desirable to provide a torque transmitting shaft having more than a single torsional stiffness rate.